Quantum corrections to leptogenesis from the gradient expansion

TL;DR

This paper uses the closed-time-path formalism to calculate gradient corrections to leptogenesis kinetic equations, revealing an additional CP-violating source term that can dominate under certain conditions.

Contribution

It introduces a new gradient correction to leptogenesis equations, showing an additional CP-violating source term arising even in local thermal equilibrium.

Findings

The additional source term is proportional to the universe's expansion rate.

In standard thermal leptogenesis, the correction is small.

The correction can dominate in ultra-strong washout scenarios.

Abstract

Using the closed-time-path formalism we quantify gradient corrections to the kinetic equations for leptogenesis, that are neglected in the standard Boltzmann approach. In particular we show that an additional CP-violating source term arises, which is non-zero even when all species are in local thermal equilibrium. In the early universe it is proportional to the expansion rate and would vanish for static equilibrium configurations, in accordance with the Sakharov conditions. We find that for thermal leptogenesis in a standard cosmological background the additional source term is small. However, it can become the dominant source in the limit of ultra-strong washout.